在.Net的MVC开发中，经常会使用到Json对象，于是，系统提供了JsonResult这个对象，其本质是调用.Net系统自带的Json序列化类JavaScriptSerializer对数据对象进行序列化。但是这个系统自带的Json序列化对象方法没有Json.Net好用，于是打算有些时候用Json.Net替代默认的实现。
要实现有时候用Json.Net，有时候用默认实现，那么就要保证系统中两种实现并存。对于Server将对象序列化成Json传给Client很简单，我们只需要建立一个新的ActionResult，我们命名为JsonNetResult，然后在Get时，return这个JsonNetResult即可。JsonNetResult的代码实现为：
using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace MvcJsonNet { using System.IO; using System.Web; using System.Web.Mvc; using Newtonsoft.Json; public class JsonNetResult : JsonResult { public JsonNetResult() { Settings = new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Error }; } public JsonNetResult(object data, JsonRequestBehavior behavior = JsonRequestBehavior.AllowGet, string contentType=null, Encoding contentEncoding=null) { this.Data = data; this.JsonRequestBehavior = behavior; this.ContentEncoding = contentEncoding; this.ContentType = contentType; } public JsonSerializerSettings Settings { get; private set; } public override void ExecuteResult(ControllerContext context) { if (context == null) throw new ArgumentNullException("context"); if (this.JsonRequestBehavior == JsonRequestBehavior.DenyGet && string.Equals(context.HttpContext.Request.HttpMethod, "GET", StringComparison.OrdinalIgnoreCase)) throw new InvalidOperationException("JSON GET is not allowed"); HttpResponseBase response = context.HttpContext.Response; response.ContentType = string.IsNullOrEmpty(this.ContentType) ? "application/json" : this.ContentType; if (this.ContentEncoding != null) response.ContentEncoding = this.ContentEncoding; if (this.Data == null) return; var scriptSerializer = JsonSerializer.Create(this.Settings); using (var sw = new StringWriter()) { scriptSerializer.Serialize(sw, this.Data); response.Write(sw.ToString()); } } } }
要返回一个Json.Net序号列后的对象，那么调用方法是：
[HttpGet] public ActionResult GetJsonNet() { var myClass = InitClass(); return new JsonNetResult(myClass); }
这是Get方法，但是对于ClientPost一个Json回Server，那么就比较麻烦了，需要修改好几处地方：
1，建立Json.Net的ValueProviderFactory，这个类主要就是用于Json字符串的反序列化。
using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace MvcJsonNet { using System.Collections; using System.Dynamic; using System.Globalization; using System.IO; using System.Web.Mvc; using System.Web.Script.Serialization; using Newtonsoft.Json; public class JsonNetValueProviderFactory : ValueProviderFactory { private void AddToBackingStore(Dictionary<string, object> backingStore, string prefix, object value) { IDictionary<string, object> d = value as IDictionary<string, object>; if (d != null) { foreach (KeyValuePair<string, object> entry in d) { AddToBackingStore(backingStore, MakePropertyKey(prefix, entry.Key), entry.Value); } return; } IList l = value as IList; if (l != null) { for (int i = 0; i < l.Count; i++) { AddToBackingStore(backingStore, MakeArrayKey(prefix, i), l[i]); } return; } // primitive backingStore[prefix] = value; } private object GetDeserializedObject(ControllerContext controllerContext) { if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.InvariantCultureIgnoreCase)) { // not JSON request return null; } StreamReader reader = new StreamReader(controllerContext.HttpContext.Request.InputStream); string bodyText = reader.ReadToEnd(); if (String.IsNullOrEmpty(bodyText)) { // no JSON data return null; } //接下来的代码是关键，判断content type，如果是json.net，那么就使用Json.Net的反序列化方法，如果不是，那么就使用系统默认的反序列化方法 if (controllerContext.HttpContext.Request.ContentType.StartsWith("application/json.net", StringComparison.InvariantCultureIgnoreCase)) { var jsonData = JsonConvert.DeserializeObject<ExpandoObject>(bodyText); return jsonData; } else { JavaScriptSerializer serializer = new JavaScriptSerializer(); object jsonData = serializer.DeserializeObject(bodyText); return jsonData; } } public override IValueProvider GetValueProvider(ControllerContext controllerContext) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } object jsonData = GetDeserializedObject(controllerContext); if (jsonData == null) { return null; } Dictionary<string, object> backingStore = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); AddToBackingStore(backingStore, String.Empty, jsonData); return new DictionaryValueProvider<object>(backingStore, CultureInfo.CurrentCulture); } private string MakeArrayKey(string prefix, int index) { return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]"; } private string MakePropertyKey(string prefix, string propertyName) { return (String.IsNullOrEmpty(prefix)) ? propertyName : prefix + "." + propertyName; } } }
2，在初始化MVC时替换掉默认的JsonValueProviderFactory。
在Global.asax的Application_Start时，写入以下代码：
ValueProviderFactories.Factories.Remove(ValueProviderFactories.Factories.OfType<JsonValueProviderFactory>().FirstOrDefault());
ValueProviderFactories.Factories.Add(new JsonNetValueProviderFactory());
3，建立新的ModelBinder，命名为JsonNetModelBinder。
namespace MvcJsonNet { using System; using System.ComponentModel; using System.Diagnostics; using System.Globalization; using System.Linq; using System.Web.Mvc; using Newtonsoft.Json; public class JsonNetModelBinder : DefaultModelBinder { protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) { Debug.WriteLine("BindProperty"); if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json.net", StringComparison .InvariantCultureIgnoreCase)) { //根据Content type来判断，只有json.net这种content type的才会使用该ModelBinder，否则使用默认的Binder base.BindProperty(controllerContext, bindingContext, propertyDescriptor); return; } // need to skip properties that aren't part of the request, else we might hit a StackOverflowException string name = propertyDescriptor.Name; foreach (object attribute in propertyDescriptor.Attributes) { if (attribute is JsonPropertyAttribute) { var jp = attribute as JsonPropertyAttribute; name = jp.PropertyName; } } string fullPropertyKey = CreateSubPropertyName(bindingContext.ModelName, name); if (!bindingContext.ValueProvider.ContainsPrefix(fullPropertyKey)) { return; } // call into the property's model binder IModelBinder propertyBinder = Binders.GetBinder(propertyDescriptor.PropertyType); object originalPropertyValue = propertyDescriptor.GetValue(bindingContext.Model); ModelMetadata propertyMetadata = bindingContext.PropertyMetadata[propertyDescriptor.Name]; propertyMetadata.Model = originalPropertyValue; var innerBindingContext = new ModelBindingContext { ModelMetadata = propertyMetadata, ModelName = fullPropertyKey, ModelState = bindingContext.ModelState, ValueProvider = bindingContext.ValueProvider }; object newPropertyValue = GetPropertyValue(controllerContext, innerBindingContext, propertyDescriptor, propertyBinder); propertyMetadata.Model = newPropertyValue; // validation ModelState modelState = bindingContext.ModelState[fullPropertyKey]; if (modelState == null || modelState.Errors.Count == 0) { if (OnPropertyValidating(controllerContext, bindingContext, propertyDescriptor, newPropertyValue)) { SetProperty(controllerContext, bindingContext, propertyDescriptor, newPropertyValue); OnPropertyValidated(controllerContext, bindingContext, propertyDescriptor, newPropertyValue); } } else { SetProperty(controllerContext, bindingContext, propertyDescriptor, newPropertyValue); // Convert FormatExceptions (type conversion failures) into InvalidValue messages foreach ( ModelError error in modelState.Errors.Where(err => String.IsNullOrEmpty(err.ErrorMessage) && err.Exception != null) .ToList()) { for (Exception exception = error.Exception; exception != null; exception = exception.InnerException) { if (exception is FormatException) { string displayName = propertyMetadata.GetDisplayName(); string errorMessageTemplate = "The value '{0}' is not valid for {1}."; string errorMessage = String.Format(CultureInfo.CurrentCulture, errorMessageTemplate, modelState.Value.AttemptedValue, displayName); modelState.Errors.Remove(error); modelState.Errors.Add(errorMessage); break; } } } } } } }
4，建立一个VModel的基类，为该基类添加Attribute，然后在Global中添加Model和Binder的映射。
[ModelBinder(typeof (JsonNetModelBinder))] public abstract class VEntity { public virtual long Id { get; set; } }
Global.asax中Application_Start添加代码：
ModelBinders.Binders.Add(typeof(VEntity), new JsonNetModelBinder());
5在前端Post Json时，指定content type为application/json.net
function PostJsonNet() { var jsonstr = $("#jsonstring")[0].innerHTML; $.ajax({ url: "MyTest/CreateFromJsonNet", type: "POST", data: jsonstr, contentType: "application/json.net", dataType: "json", success: function (data) { alert(data); } }); }
我们这样处理后，Client在往Server传送Json数据时，如果指定了contentType是application/json，那么就使用系统默认的方法来反序列化对象，如果是application/json.net，那么就使用Json.Net来反序列化。
